Minimization of the time between injury occurrence and transport to the appropriate level of medical care is necessary to ensure that wounded and sick soldiers obtain the prompt medical attention essential for their survival. During that time, aeromedical care in a MEDEVAC™ medical evacuation helicopter environment is used to identify and transport casualties.
Military units conduct aeromedical evacuations daily during times of war and peace, exposing the patient and flight/medical crew to noise or environmental stress and difficult monitoring conditions. As in the civilian community, military nurses depend on reliable and efficient monitoring devices to provide accurate patient care in various environments, some of which are hostile and obtrusive to the use of conventional monitoring instrumentation. While aeromedical evacuation is a life-saving process for many, it is nearly impossible for medical personnel to monitor vital signs in a high noise environment.
Vital signs monitoring is normally a simple and routine procedure involving collection of pulse, respiration and blood pressure data. In a relatively quiet environment, these parameters are easily detected. However, acquisition of physiological signals of interest in a helicopter environment is a challenging problem for several reasons. Limitations on vital signs collection include high noise, vibration, auditory distractions, ineffective monitoring equipment, cramped working conditions, bulky gear during air evacuation, and electromagnetic interference with aircraft systems caused by some medical equipment. The additional complexity of leads and electrodes compounds the noise and environmental problems. The physiological parameters of vital signs fall within the helicopter-generated frequencies. Helicopter frequencies have a much greater power in those frequencies as well. Vibrational and acoustic artifacts are also major problems. The signal to noise problem must therefore be solved by other means in addition to low and high band pass filtering approaches. Due to the limiting work conditions, medical personnel cannot use a stethoscope to accurately monitor heart activity or blood pressure.
The military medical system needs a portable, non-invasive device capable of monitoring a soldier's vital signs in the field environment under less than ideal circumstances. This system needs to be useful to military medical personnel across the spectrum of care delivery, such as in mass casualty situations, aeromedical evacuations, ground ambulance transports, hospital wards, and intensive care units. A recent study found that thirty-two percent of aircraft medical devices flown onboard a rotor-wing MEDEVAC aircraft failed at least one environmental test.
Quartz crystals are minerals that create an electric field known as piezoelectricity when pressure is applied. Materials scientists have found other materials with piezoelectric properties. The versatility and potential uses for piezoelectric materials have been known but cost-prohibitive for some time.
However, recent decreases in the cost of manufacturing now permit greater application by engineers and researchers. The advantageous qualities of piezoelectric materials have been applied to medicine, security, acoustics, defense, geology and other fields. Development of applications with piezoelectric materials is in its infancy.
The medical practice and research application of piezoelectric-based instrumentation is gaining momentum. Piezoelectric methods have been successfully used in plethysmography, blood pressure monitoring by piezoelectric contact microphone, heart rate monitoring in avian embryos and hatchlings and piezoelectric probes. Piezoelectric materials are used as detectors of sensitive motion to measure human tremor, small body movements of animals in response to pharmacological manipulation, and respiratory motion for nuclear magnetic resonance (NMR) animal experiments. In combination with ultrasound, piezoelectric methods have been used to assess coronary hemodynamics, elastic tensor, intra-arterial imaging, and receptor field dimensions. In addition, piezoelectric transducers have been attached to the chest wall and used with automated auscultation devices and microcomputers for lung sound analysis. Piezoelectric film has been applied and studied to determine joint contact stress, and piezoelectric disks have been used for recording muscle sounds and qualitative monitoring of the neuromuscular block.
Stochastic wave theory, as commonly used in ocean engineering to analyze pseudo-periodic phenomena, indicates spectral peaks from respiration and heart rate. Human heartbeats, respiration, and blood pressure are repetitive in nature, reflecting complex mechano-acoustical events. However, various problems with piezoelectric instrumentation development prevent its full realization. Measurement of human tremor only works well when the environment is absolutely silent. In fact, extraneous noise such as equipment, fans, people talking, and the patient's own voice routinely exists in most hospital rooms. That noise masks and distorts the signal of interest, thus limiting the practicality of piezoelectric instrumentation. Animal noises make data collection difficult in laboratory animal studies. In non-laboratory environments, medical uses of piezoelectric instrumentation for humans remains a problem because of the inherent signal-noise problem.
A primary mission of military nurses is to ensure that wounded and sick soldiers obtain prompt medical attention and/or evacuation to definitive medical care. The actions performed during the time period between a battlefield injury and the transfer of casualties to appropriate medical treatment is critical for the welfare of the soldier, and can be the difference between life and death. It is during this critical time period where diagnosis and treatment begins and also when evacuation—for example via MEDEVAC™ medical evacuation helicopter—occurs.
Unfortunately, the extremely high noise and vibration inherent in the helicopter environment prevents nursing and medical personnel from accurately measuring vital signs. Not only are electronic medical monitors rendered ineffective with the high vibrations; traditional methods of measuring pulse and blood pressure using a stethoscope become unreliable in the high noise. Cramped working conditions and bulky gear during air evacuation exacerbate these problems.
Most conventional methods use devices that employ electrodes, leads, wires, and cuffs to measure one or more vital signs, for example, blood pressure machine, ECG monitor, pulse oximeter. Existing monitors require some sort of attachment and thus are not passive. In addition, conventional equipment is highly sensitive to noise, such as a helicopter or airplane engines and rotors.
Clearly, what is needed for this common situation is a monitor that can consistently and accurately measure vital signs during a medical evacuation where there is high noise and vibration. The monitor being relatively autonomous intervention by a nurse or technician is not required. With the added capability of telemetry for remote monitoring and communication, information may be forwarded in real-time via wireless communication to the destination where medical personnel and other caregivers are located.
Needs exist to develop better methods and apparatus for physiological monitoring.